In planta production of apoplast-targeted cellulose degrading enzymes may be a valuable approach for efficient production of concentrated enzyme preparations that can be used for saccharification of cellulose in pretreated feedstocks. The use of agroinfiltration to produce heterologous proteins of interest (POI) in leaf tissue has been reviewed along with considerations affecting yield and downstream processing (Menkhaus T J et al., Biotechnology Progress, 20, 2004, 1001-1014). The benefits of obtaining a purified extract from plant tissue have been discussed previously (Hassan S et al., Plant Biotechnology Journal, 6, 2008, 733-748; Wilken L R et al., Biotechnology Advances, 30, 2012, 419-433), and a method for recovering apoplast wash fluid from leaf tissue has been described (Klement Z, Phytopathology, 55, 1965, 1033; Rathmell W G et al., Plant Physiology, 53, 1974, 317-318). However, traditional recovery methods, such as tissue homogenization, suffer from disadvantages including that high fiber content fouls chromatography columns, equipment is and operating costs are expensive, there is an increased likelihood of contaminant release, and air-liquid interfaces may damage protein (Hassan S et al., 2008, Plant Biotechnology Journal, 6, 733-748). Previous reports have used apoplast wash fluid (AWF) recovery to remove secreted recombinant POI from leaf tissue and quantified its recovery as a percent yield of the total protein expressed (Turpen T H et al., U.S.P. Office (Ed.), Large Scale Biology Corporation, USA, 2006, pp. 28; Lombardi R et al., Transgenic Research, 19, 2010, 1083-1097). However, protein degradation in leaf tissue, especially in the leaf apoplast, remains a major industrial impediment (Hehle V K et al., BMC Biotechnology, 2011; Doran P M, Trends in Biotechnology, 24, 2006, 426-432). Thus, there exists a need for improved methods of increasing the production and recovery of a protein of interest from the apoplast of plant tissues.